tireheight.comHow to read a tire size
285 is the width in millimeters, 70 is the sidewall height as a percentage of the width, R means radial, and 17 is the wheel diameter in inches. Worked through, that's 11.2″ wide and 32.7″ tall. The tire makers list 285/70R17 tires at 32.70–33.15″.
Each part of LT285/70R17 121Q
Marks a light truck (LT) tire. P marks a P-metric (passenger) tire; no letter means Euro-metric.
Not a measurement: the sidewall is 70% as tall as the tire is wide. 70% of 285 mm is 199.5 mm, or 7.85″.
Radial construction.
121 = 3,195 lb per tire, from the standard load index table.
Q = up to 99 mph, from the standard speed rating table.
From size to height
The height comes from the wheel plus two sidewalls.
| Step | 285/70R17 |
|---|---|
| Width: 285 mm ÷ 25.4 | 11.22″ |
| Sidewall: 285 mm × 70% ÷ 25.4 | 7.85″ |
| Height: 17 + 2 × 7.85 | 32.71″ |
| Listed by BFGoodrich, General, Michelin, Mickey Thompson and Toyo (36 tires) | 32.70–33.15″ |
The size code gives one height; the tires don't share it. Across the 414 sizes on this site with two or more tires, the listed heights within a size differ by 0.10″ at the median, by 0.25″ or more in 99 sizes, and by up to 0.84″ in 285/65R18. 285/70R17 counts as a 33-inch tire.
Sizes written in inches: 35×12.50R17
Flotation sizes give the height first.
35 inches tall on paper. The 18 35×12.50R17 tires here are listed at 34.50–35.00″.
12.50 inches wide.
Questions
How do you read a tire size?
Take 285/70R17: 285 is the width in millimeters (11.22″), 70 is the sidewall height as a percentage of that width (7.85″), R means radial construction, and 17 is the wheel diameter in inches. Together they give a height of 32.71″ on paper.
What does the 70 mean in 285/70R17?
It's the aspect ratio: the sidewall is 70% as tall as the tire is wide. 70% of 285 mm is 199.5 mm, or 7.85″.
How tall is a 285/70R17 tire?
32.71″ from the size code. The 36 285/70R17 tires from BFGoodrich, General, Michelin, Mickey Thompson and Toyo on this site are listed at 32.70–33.15″.
How do you read a size like 35×12.50R17?
It's a flotation size, given in inches: 35″ tall, 12.50″ wide, for a 17″ wheel. The 18 tires in that size here are listed at 34.50–35.00″ tall.
How do you work out a tire's height from its size?
Wheel diameter + 2 × sidewall height. For 285/70R17: 17 + 2 × 7.85 = 32.71″. Listed heights differ from this: across the 414 sizes on this site with two or more tires, the gap between the shortest and tallest listed tire is 0.10″ at the median and up to 0.84″ (285/65R18).